There is a known method of rubber waste processing (RU Patent No. 2076501, IPC B29B17/00, C08J11/10, C 08J11/14. Published Mar. 27, 1997).
The method includes thermal decomposition of rubber waste in a working fluid consisting 98-85 wt. % of water vapor superheated to 300-1600° C. and 2-15 wt. % of gas obtained after the separation of oil from gaseous decomposition products. Besides, prior to thermal decomposition, rubber waste is mixed with 3-40 wt. % of oil by passing gaseous decomposition products and the working fluid through a layer of waste, their weight ratio being (0.05-1.62):1, and solid products of decomposition are mixed with 4-40 wt. % of oil and compacted into briquettes, simultaneously heating them to 100-500° C. by filtering the gas obtained after the separation of oil from gaseous decomposition products.
Among the disadvantages of this method are:
1. High specific energy consumption for the waste recycling process dictated by the use of water vapor at temperatures of up to 1600° C.
2. Large emissions to the environment of harmful combustion products of fuel used for water vapor generation and its superheating to a high temperature.
3. Low quality of the processing products, since the heavy hydrocarbon fraction containing sulfur compounds and having a high ash content is not separated from oil (liquid products), and the solid products (solid residue) containing industrial carbon are not processed but used as fuel in briquettes.
There is a known method of rubber waste processing (RU Patent No. 2245247, IPC B29B17/00, C08J11/14. Published 20 May 2004.) According to this method, the waste is processed by its thermal decomposition in a furnace, separation of decomposition products into solid and gaseous ones, separation of a liquid phase from the gaseous products, and removing the latter for burning to maintain the decomposition process. Besides, prior to thermal decomposition, the waste is mixed with 5-15 wt. % of water, and then re-mixed with water by atomizing water in the furnace in the amount of 50-150% of the waste's weight, and the solid products of decomposition are sprinkled with water in the amount of 10-20% of the rubber waste's weight. Besides, the condensate obtained by separation from liquid phase is used in place of water.
Among the disadvantages of this method are:
1. High specific energy consumption due to the heating of large amounts of water (up to 150% of the waste weight) during waste processing.
2. Large polluting emissions to the environment generated in the evaporation of condensate contaminated with hydrocarbons, which is both atomized in the furnace and used to sprinkle solid products heated to a high temperature (not lower than 300° C.).
3. Low quality of liquid and solid products of rubber waste, due to the fact that a heavy fraction containing harmful sulfur compounds (mercaptans) is not separated from liquid products, and that solid products are not processed (separated) into carbon-containing products and ash.
A process and plant for recycling rubber-containing waste is known (RU Patent No. 2460743, MΠκ C08J11/20. Published Sep. 10, 2012.)
Rubber-containing waste is processed by thermolysis of rubber granules at 350-400° C. in circulating superheated and evaporated gasoline under a pressure close to atmospheric. In doing so, rubber granules are decomposed into industrial carbon, synthetic crude oil, and hydrocarbon gas. The generated industrial carbon with absorbed oils is blown with air; in doing so, textile cord is completely burnt, some of the oil is burnt, and some carried off with flue gases.
Among the disadvantages of this method are:
1. High energy consumption of the process due to the necessity to use a circulating heat transfer agent, which has to be separated from the hydrocarbon vapors generated in the thermal decomposition of rubber, and then to be heated in a heat exchanger, evaporated, and superheated in a furnace prior to feeding to the reactor.
2. Large polluting emissions to the environment generated in the combustion of absorbed oils and textile cord. In doing so, some of the oil is carried off to the atmosphere with flue gases.
3. Low quality of industrial carbon due to oil adsorption, therefore industrial carbon is blown with air to remove some of the oil, so that the carbon surface oxidizes and its quality deteriorates. Incomplete extraction of liquid phase (oil) from the gas flow results in losing some of the valuable liquid products.
The closest to the proposed invention is the method of rubber-containing waste processing and the plant for its embodiment adopted by us as the prior art (RU Patent 2291168, IPC C08J11/04, C08J11/20, B29B17/00. Published Jan. 10, 2007.)
The method of processing of rubber-containing waste or a mixture of rubber-containing and polymer waste includes a stage of its preliminary preparation, a stage of thermal decomposition in a furnace with separation of decomposition products into vapor-gas mixture and solid residue, a stage of separation of liquid phase from the vapor-gas mixture generating hydrocarbon-containing gas, and a stage of separation of carbon-containing product from the solid residue. Furthermore, at the preliminary preparation stage, whole and/or shredded waste is blown with natural gas at the start of the first cycle of processing, and at subsequent stages, with hydrocarbon-containing gas with subsequent impregnation with a hydrocarbon solvent, i.e. liquid hydrocarbon fraction with a boiling point not higher than 220° C. for at least 15 minutes, where the stage of thermal decomposition in the first cycle takes place in natural gas heated to 400-500° C., and in subsequent cycles in hydrocarbon-containing gas heated to 400-500° C.; the liquid phase is separated from the vapor-gas mixture in three stages, the vapor-gas mixture being cooled to 300-360° C. at the first stage with subsequent separation of a heavy hydrocarbon fraction, and to a temperature not exceeding 220° C. at the second stage with subsequent separation of a hydrocarbon fraction and recirculation of a part thereof to the stage of preliminary waste preparation to be used as hydrocarbon solvent, while at the third stage, the vapor-gas mixture is cooled to a temperature below 30° C. with subsequent separation of a light hydrocarbon fraction; the hydrocarbon-containing gas generated after the liquid phase separation from the vapor-gas mixture is separated into at least four flows, one of which is directed to combustion for heating the second flow of hydrocarbon-containing gas, which is fed into the furnace for the thermal decomposition stage, the third flow being used for blowing at the preliminary waste preparation stage, and the fourth flow being supplied to the user; the solid residue is blown with air and cooled before the hydrogen-containing product separation stage, and the gases generated after the blowing at the preliminary waste preparation stage and the solid reside blowing are directed for burning to heat the second flow of hydrocarbon-containing gas.
Among the disadvantages of this method are:
1. High energy consumption due to several stages of the recycling process, no thermal energy recirculation (thermal energy recycling to the process), the need to use an additional heat transfer agent in the form of natural gas, and inevitable heat losses in the processes of heating the heat transfer agent in the heat exchanger, its evaporation, and superheating prior to feeding into the furnace.
2. Large polluting emissions to the environment generated in the air blowing of heated solid residue, resulting in oxidation of carbon and residual hydrocarbons contained in solid residue, with toxic combustion products generated.
3. Low quality of carbon-containing product due to partial oxidation in the air blowing of solid residue, which results in a higher ash content in carbon-containing product and a lower carbon content.